This relates generally to electronic devices, and more particularly, to electronic devices with displays.
Electronic devices often include displays. For example, cellular telephones and computers may have displays for presenting information to a user.
Liquid crystal displays contain a layer of liquid crystal material. Pixels in a liquid crystal display contain thin-film transistors and electrodes for applying electric fields to the liquid crystal material. The strength of the electric field in a pixel controls the polarization state of the liquid crystal material and thereby adjusts the brightness of the pixel.
Substrate layers such as color filter layers and thin-film transistor layers are used in liquid crystal displays. A thin-film transistor layer contains an array of the thin-film transistors and associated pixel electrodes that are used in controlling electric fields in the liquid crystal layer. A color filter layer contains an array of color filter elements such as red, blue, and green elements. The color filter layer provides the display with the ability to display color images.
In assembled displays, components are coupled to display substrate layers. For example, in a display in which the thin-film transistor layer forms the outermost display layer of the display, the thin-film transistor layer may have a region that extends past the edge of the color filter layer. Components such as flexible printed circuits and display driver integrated circuits may be mounted to bonding pads in this region using a material such as anisotropic conductive film (ACF).
Materials such as anisotropic conductive film are insulating before being compressed together between mating bonding pads. When pressure is applied in the region between mating pads, the film becomes conducting and forms a short circuit between the pads.
Anisotropic conductive films include particles that press into the pads during bonding. When a pad is formed on a transparent substrate, the metal layer that forms the pad can be viewed through the transparent substrate. When sufficient force is applied to a pair of mating contacts to form a satisfactory anisotropic conductive film bond, the particles in the anisotropic conductive film will tend to disrupt the metal layer. This disruption will lead to particle-shaped visual artifacts on the surface of the metal layer that is adjacent to the transparent substrate. By viewing the contacts through the substrate, the quality of the anisotropic conductive film bonds that have been formed can be evaluated. If the bonds do not appear satisfactory during inspection, the display may be scrapped or repaired.
To hide internal components from view in a display, the inactive border region of a display layer such as a thin-film transistor layer may be coated with an opaque material such as a black masking layer. The presence of the black masking layer may block viewing of the surface of the metal layer that is adjacent to the thin-film transistor layer substrate so that it is not possible to evaluate anisotropic conductive film bonds in the display.
It would therefore be desirable to be able to provide displays with improved structures for facilitating the evaluation of anisotropic conductive film bonds.